1. Technical Field
The present disclosure relates to methods for making block copolymers for use in producing surgical articles such as sutures, and more particularly to a method for making bioabsorable block copolymers by transeterifying two or more pre-polyers.
2. Background of Related Art
Methods for making monofilaments that are suitable surgical sutures generally include the steps of extruding a least one bioabsorable or nonbioabsorable polymer to provide filaments, drawing, or stretching the solidified filaments to achieve molecular orientation and annealing th edrawn filaments to relieve internal stresses. Se, e.g. U.S. Pat. Nos. 392,891, 3,106,442, 3,630,205, 4,911,165, 5,217,485 and U.K. Patent Specification No. 1,588,081 and European Patent Application No. 415,783.
Examples of copolymers used to fabricate surgical articles such as sutures include, for example, diblock copolymers, symbolized by an AB block structures, or triblock copolymers, sybolized by an ABA block structure, wherein A and B present polymeric chain having repeating units of a given type wherein the A chain and the B chain are each normally derived from different monomer components of different combinations of monomers. See, e.g., U.S. Pat. No. 4,826,945 to Cohn et al. and U.S. Pat. No. 4,438,253 to Casey et al.
Transesterification that occurs in bioabsorbable polyesters produces a high degree of shuffling and randomness which prevents the resulting transesterfied copolymer from having a well defined block structure. See, e.g., U.S. Pat. No. 5,252,701 to Jarrett et al. Such randomness also affects the properties of the final surgical product, such as in vivo strength retention as well as other chemical and physical properties such as solubility, brittleness, and rate of absorption. It would be desirable to have a simple method to make a surgical article from a bioabsorbable block copolymer through a transesterification reaction while maintaining a well defined block structure.